This disclosure relates generally to wireless communication and, more particularly, to a system and method for quality-driven channel selection in a communication network.
In a wireless communication network, such as a Time Division Multiple Access (TDMA) network, wireless communication devices, such as mobile phones, are used to initiate voice calls. In order to do so, a mobile phone is provided with a radio frequency (RF) control channel to xe2x80x9cset-upxe2x80x9d the call between the mobile phone and the destination phone via the TDMA network. Once the set-up has been completed, the mobile phone is provided with RF voice channels that include three time slots for carrying information (voice bits) between the mobile phone and the destination phone.
It is very important to ensure that the voice channel provided to the mobile phone will be one that is of high quality. If the voice channel experiences interference as it traverses through the network, the information that the voice channel is carrying may be degraded, corrupted, or lost. Thus, it is important that a channel selection method chooses the channels with little or no interference to be utilized in the network.
There are several known channel selection methods including fixed channel assignment and dynamic channel assignment. In the fixed channel assignment method, channels are only utilized in conjunction with their respective base stations so as to not cause interference on the basis of the predictive results of propagation characteristics. In the dynamic channel assignment method, a channel is selected for every communication so as to not cause interference. Thus, channels are free to be used as long as interference is prevented thereby allowing more users to utilize the wireless communication network. For this reason, the use of the dynamic channel assignment method is increasing.
U.S. Pat. No. 5,771,454 by Ohsawa, describes a wireless communication network that utilizes a dynamic channel assignment method. In this method, base station coverage areas hierarchically overlap each other and the communication channels within these areas are used commonly by the hierarchies. When a request for communication arises, each base station performs selection from within the same hierarchy, and in this instance, a channel with which selection is to be begun is offset between the different hierarchies. Each base station controls the offset value based on a blocking occurrence value and/or a hand-over failure occurrence number of the base station so that it may be decreased in a hierarchy whose value or values mentioned are comparatively high.
U.S. Pat. No. 5,280,630 by Wang, also describes a wireless communication network that utilizes a dynamic channel assignment method. In this method, a channel allocator accesses a preferred channel list to allocate communication channels. The preferred channel list ranks channels in accordance with the occurrence of prior events on the channels, such as interrupted calls, blocked call setup requests, and calls successfully completed, ans in regards to a mean quality margin and the current channel quality.
Although a large number of users can be accommodated when a dynamic channel assignment method is utilized, complicated control schemes and apparatus arrangements are required. Additionally, interference between the base station coverage areas may occur because of the channel allocation methods used. These limitations degrade the quality and the efficiency of the system.
U.S. Pat. No. 5,507,008 by Kanai and Hamabe, describes a wireless communication network in which a channel assignment method that utilizes a carrier to interference ratio is used. Each of the base stations in the cells of the network, selects one of all speech communication channels in an order of priority common to all the cells. A base station then checks whether the carrier to interference ratio of the selected speech communication channel is equal to or higher than a predetermined level. The selected channel is assigned as a speech communication channel for the call when it is determined on the basis of the check result that the carrier to interference ratio is equal to or higher than the predetermined level. Although the carrier to interference ratio is used in determining channel selection, other important variables are not utilized. Thus, the ability of a base stations to select the highest quality channels is limited.
Therefore, it is an object of the present invention to provide a system and method for quality-driven channel selection in a communication network that overcome the limitations described above. In one embodiment, the method measures interference on idle and active voice channels in a first quality-driven channel selection (QCS) cell. The method then automatically orders a voice channel queue based on a clearest voice channel (which is determined by reverse bit error rate (RBER) measurements and forward bit error rate (FBER) measurements on the active voice channels and by idle noise measurements on the idle voice channels). Dynamic channel sets (DCS) are then created from the voice channel queue based on the RBER, FBER, and idle noise received, where the DCS are queues that include low interference channels and moderate interference channels. The prioritization of the channels does not change during the call but is prioritized after the call has been completed. As such, the latest measurements are taken into account to properly prioritize the channel with the highest quality to be used for the next incoming call.
A dynamic channel assignment method is not used with the present invention thus removing the limitations described above. The present invention assists the customer in engineering the system for minimum interference, as the system automatically prioritizes channels (after frequency planning has been performed) to reduce noise on newly allocated calls and relieves the customer of having to continually monitor the channels selected to minimize interference in a changing environment. Additionally, the noise on newly allocated calls is reduced providing an increase in transmission quality.
These objects, as well as others which will become apparent, are achieved in a system that includes a plurality of wireless communication devices that communicate with a plurality of base transceiver stations (BTSs or base stations), a plurality of base station controllers (BSCs) that are coupled to the BTSs and a plurality of Mobile Switching Center""s (MSCs) that are coupled to the BSCs.